This invention relates, in general, to perforating a subterranean wellbore using shaped charges and, in particular, to a bi-directional explosive transfer subassembly that is installed within a work string between loaded perforating guns for use in deviated wellbores.
Without limiting the scope of the present invention, its background will be described with reference to perforating a subterranean formation using shaped charge perforating guns, as an example.
After drilling the section of a subterranean wellbore that traverses a formation, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within the wellbore. This casing string increases the integrity of the wellbore and provides a path for producing fluids from the producing intervals to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string, hydraulic opening or perforation must be made through the casing string, the cement and a short distance into the formation.
Typically, these perforations are created by detonating a series of shaped charges located within the casing string that are positioned adjacent to the formation. Specifically, numerous charge carriers are loaded with shaped charges that are connected with a detonating device, such as detonating cord, forming perforating guns. The perforating guns are then connected within a tool string that is lowered into the cased wellbore. Once the perforating guns are properly positioned in the wellbore such that the shaped charges are adjacent to the formation to be perforated, the shaped charges are detonated. Upon detonation, each shaped charge creates a jet that blasts through a scallop or recess in the charge carrier, creates a hydraulic opening through the casing and cement and then penetrates the formation forming a perforation therein. Typically, the shaped charges are fired from the near end to the far end of the formation. In the event of a misfire of the shaped charges, however, it may be necessary to reverse the firing sequence to fire the shaped charges from the far end to the near end of the formation.
It has been found that it is sometimes difficult to deploy the desired length of perforating guns into highly deviated or horizontal wells and wells with restrictions. Specifically, in such well configurations, large bending moments act on the string of perforating guns in the plane parallel to the centerline of the perforating guns. These large bending moments can cause failures at the connections between perforating guns, which may result in misfiring. In addition, these large bending moments can prevent relative rotation of the perforating guns about the centerline of the perforating guns such that it is difficult or impossible to orient the perforating guns to fire in the desired direction.
A need has therefore arisen for an apparatus that allows a string of perforating guns to be run into highly deviated or horizontal wells and wells with restrictions. A need has also arisen for such an apparatus that allows for the proper orientation of the perforating guns so that they fire in the desired direction. Further, a need has arisen for such an apparatus that allows for bi-directional firing of the perforating guns.
The present invention disclosed herein comprises a bi-directional explosive transfer subassembly that can be installed within a tool string between two live perforating guns that allows a string of perforating guns to be deployed into a highly deviated well, a horizontal well or a well with restrictions. In addition, the bi-directional explosive transfer subassembly of the present invention allows for the proper orientation of the perforating guns so that they fire in the desired direction.
The bi-directional explosive transfer subassembly of the present invention comprises a first explosive carrying member having a ball end and a first explosive cavity and a second explosive carrying member having a socket and a second explosive cavity. The ball end of the first explosive carrying member is slidingly received in the socket of the second explosive carrying member such that the first and second explosive carrying members are rotatable and angularly displaceable relative to one another. A first explosive device including, for example, a first shaped charge is disposed in the first explosive cavity. A second explosive device including, for example, a second shaped charge is disposed in the second explosive cavity. The first and second explosive devices are spaced apart such that the first and second shaped charges face one another and are each adapted for sending an explosive jet toward the other shaped charge, thereby providing an explosive transfer therebetween. Accordingly, when one of the first and second explosive devices is initiated, the other of the first and second explosive devices will in turn be initiated.
The first explosive carrying member of the bi-directional explosive transfer subassembly may include a cylindrical portion extending integrally from the ball end. The second explosive carrying member may include a flange portion extending from the socket that has a conically shaped inner surface having an angle that defines the maximum allowable angular displacement between the first and second explosive carrying members. Specifically, the maximum allowable angular displacement occurs when the cylindrical portion of the first explosive carrying member contacts the flange portion of the second explosive carrying member. The maximum angular displacement between the first and second explosive carrying members may be between about 1 and about 10 degrees and is preferably about 5 degrees.
The first and second explosive cavities of the bi-directional explosive transfer subassembly are separated by portions of the first and second explosive carrying members. For example, the first and second explosive carrying members may respectively include first and second wall portions that are adjacent to one another, thereby separating the first and second explosive cavities. Both the first and second explosive devices of the bi-directional explosive transfer subassembly may include a booster, a length of detonating cord connected to the booster and a detonating cord initiator connected to the detonating cord.
In one embodiment, the bi-directional explosive transfer subassembly is positioned between first and second perforating guns in a well perforating apparatus. In this embodiment, the sliding engagement between the ball end of the first explosive carrying member in the socket of the second explosive carrying member provides for rotation and angular displacement of the first and second perforating guns relative to one another. Also in this embodiment, when one of the first and second explosive devices is initiated, the other of the first and second explosive devices will in turn be initiated thereby transferring explosive between the first and second perforating guns.
The bi-directional explosive transfer subassembly is also used in a method of perforating a well. Specifically, the method comprises deploying a string of perforating guns in a wellbore, the string having first and second perforating guns with a bi-directional explosive device disposed therebetween providing relative rotation and angularly displace therebetween. The method also comprises firing one of the first and second perforating guns, igniting one of the first and second explosive devices, igniting the other of the first and second explosive devices and firing the other of the first and second perforating guns, thereby transferring the explosive and sequentially firing the string of perforating guns.